Poster: Late and Moved Abstracts

Abs # 998: Characterization of a family of SCF E3 ligases involved in auxin response in Arabidopsis.

Presenter:	Dharmasiri, Sunethra , sdharmas@bio.indiana.edu
Authors	Dharmasiri, Sunethra  (A)   Dharmasiri, Nihal  (A)   Estelle, Mark  (A)
Affiliations:	(A): Department of Biology, Indiana University

Plant responses to the phytohormone auxin require regulated degradation of AUX/IAA proteins. In Arabidopsis, this process is mediated by the SCF^TIR1 ubiquitin E3 ligase complex consisting of CUL1, ASK1/ASK2, RBX1 and the F-box protein, TIR1. However, knockout mutants of TIR1 show mild auxin resistant phenotypes. The Arabidopsis genome contains five genes related to TIR1, designated as LRF (Leucine-rich Repeat Fbox) genes. Here we report the involvement of the LRF1, LRF2 and LRF3 genes in auxin response in Arabidopsis. Immunoprecipitation and pull down assays indicate that LRF proteins form stable SCF complexes similar to SCF^TIR1, and that AUX/IAA proteins interact with TIR1 and LRFs in an auxin-dependent manner. The expression of TIR1 and the LRFs was studied using RT-PCR and promoter-GUS fusion constructs. The results indicate that they are expressed in both root and aerial tissues. T-DNA insertion lines were isolated for LRF1, LRF2 and LRF3 to study the genetic interaction between TIR1 and the LRFs. A series of double, triple and quadruple mutants were generated between tir1, lrf1, lrf2 and lrf3 lines. Introduction of either lrf2 or lrf3 enhanced the auxin resistant root phenotype of tir1. A large fraction of the triple mutant (tir1, lrf2 lrf3) and the quadruple mutant (tir1,lrf1, lrf2, lrf3) plants showed seedling lethal phenotypes, associated with the lack of primary root growth or severely retarded roots with defective root meristem regions. Analysis of the root meristem, and the induction and stability of AUX/IAA proteins in triple and quadruple mutants will also be presented.